Although religious freedom is enshrined in the communist country's constitution, it does not exist in practice and religious activity is severely restricted to officially recognised groups linked to the government.

Pyongyang views foreign missionaries as seditious elements intent on fomenting unrest and those who are caught engaging in any activities in the North are subject to immediate arrest.

A number of missionaries - mostly US citizens - have been arrested in the past with some allowed to return home after interventions by high-profile US figures.

Pyongyang is currently holding US citizen Kenneth Bae, described by a North Korean court as a militant Christian evangelist.

He was arrested in November 2012 and later sentenced to 15 years' hard labour on charges of seeking to topple the government.

A South Korean missionary has also been detained since last October.

Kim Jeong-Wook, in a televised press conference staged in Pyongyang last, "confessed" to anti-government activities including helping organise underground churches for North Korean refugees in China and spying for Seoul's intelligence authorities.